CDMA cellular systems (such as IS-95 and CDMA2000 systems) typically require relatively precise timing between a base station and a mobile terminal (MT) to maintain proper synchronization. The MT downloads system timing information from the base transceiver station (BTS), and uses this to set the timing offset of its internal spreading code generators. At the BTS, the RAKE receiver adjusts its internally generated pseudonoise (PN) code offset to match that of the MT. Since terrestrial cells are typically about 1 km in radius, the path delay uncertainty between the MT and BTS typically requires a search range of a few chip periods for the gateway receiver to precisely synchronize to the MT's spreading code.
Compared to the terrestrial environment, CDMA operation using a satellite may introduce a much longer path delay, and also a much greater delay variability due to the larger spot beam coverage areas. For example, beam sizes typical of geosynchronous mobile communications satellites may produce a round-trip delay dispersion on the order of 5 msec within beams located over the northern continental United States (CONUS). Given a CDMA chip period of 0.814 msec, this may require the gateway receiver (or other portion of the satellite system that processes signals from MTs) to search over more than ±3000 chips to synchronize, which may be beyond the capability of conventional receivers.